Our objective is to develop, evaluate, and utilize several ultrasonic techniques for the measurements of blood flow and cardiac dimensions in acute and chronically instrumented animal models of cardiovascular disease. The four proposed developments are: 1) miniaturized pulsed Doppler flow probes 0.5 to 1.5 mm diameter for sensing blood flow through regional vessels in chronically instrumented rats, 2) flexible pulsed Doppler flow probes (1 to 8 mm diameter) for chronic implantation in young animals (rats and puppies) which may grow during the implant period, 3) a small, short range pulse-echo system to measure cardiac dimensions (chamber size and wall thickness) in small, chronically instrumented animals (rats, cats and puppies), and 4) an ultrasonic phase-shift flowmeter for measuring cardiac output in acute and chronically instrumented dogs. All of the instruments will be designed for incorporation into a single compatible system so that all devices can be operated simultaneously in a given experiment. Several applications for these techniques have been identified and include: 1) the measurement of regional blood flow, cardiac output, and ventricular dimensions and function in spontaneously hypertensive rats as a function of age, hypertensive state, treatment regimen, and pharmacologic intervention, 2) the response in conscious puppies of cardiac output, regional blood flows, and ventricular function to various clinically used drugs as a function of age, 3) the measurement of cardiac output and the evaluation of ventricular hypertrophy and failure created by aortic banding or subclavian to pulmonary artery shunting in chronically instrumented cats, 4) the measurement of cardiac output, coronary blood flow, and cardiac function in dogs before, during, and after ischemic cardiac arrest and cardiopulmonary bypass using procedures relevant to cardiac surgery in man.